1. Field of the Invention
This invention relates to an image taking apparatus having an edge enhancing function and an electronic zooming function, and also to a method for automatically controlling an edge enhancing level of an original image signal in conjunction with an electronic zooming rate.
2. Description of the Related Art
An image taking apparatus such as one applied to a digital still camera, a video camera for medical use and the like is equipped with an edge enhancing function for enhancing edges of an original taking image signal for the purpose of improving the sharpness of the original taking image, and an electronic zooming function for enlarging the extracted part of the taking image by digital processing. Please see Japanese Laid-Open Patent JP2000-278592, for example.
Edge enhancing means for performing the above mentioned edge enhancing function in the image taking apparatus generates an edge signal, as shown in FIG. 6B, based on an original image signal, as shown in FIG. 6A, and outputs an edge-enhanced image signal, as shown in FIG. 6C, by superposing the thus obtained edge signal onto the original image signal. Thereby, the edge-enhanced image signal to which an edge enhancing signal 84 is superposed at the edge portion located on the periphery of the original image signal 82 is obtained, as shown in FIG. 8A. Accordingly, the sharpness of the whole image signal is improved.
In addition, electronic zooming means for performing the above mentioned electronic zooming function extracts a part of the original image signal, that is, 4 pixels of the original image signal, as shown in FIG. 7A, for example, and enlarges these 4 pixels of the original image signal at a predetermined magnification rate, that is, 2 times in this case, in the vertical and horizontal directions. As the result, it is able to obtain the enlarged, original image signal, as shown in FIG. 7B.
However, according to such a conventional image taking apparatus, in the case of performing an enlarging processing of 2 times, for example, by the electronic zooming means to the image signal after the edge of the image signal is enhanced by the edge enhancing means, as shown in FIG. 7, an image portion 86 is magnified by 2 in the vertical and horizontal directions as shown in FIG. 8B, and an edge enhancing signal 88 is also magnified by the same magnification rate. If the edge enhancing signal 88 is magnified by 2 times, as described above, the edge signal for enhancing the sharpness of the taking image signal is magnified more than necessary, so that there is a problem that the enlarged image signal becomes an edge-enhanced image having wide and unnatural edges as compared to a desirable output image signal.
This invention was created to solve the above mentioned problems, and one aspect of the present invention is to present an image taking apparatus and a method of controlling an edge enhancing level of an original image signal capable of obtaining an enlarged image signal having natural edges by suppressing the enlargement of the edge signal to be added to the original image signal when carrying out zooming processing of the edge-enhanced image signal.